Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
In a wireless communication system, a base station may provide one or more directional or omnidirectional coverage areas in which the base station may serve user equipment devices (UEs), such as cell phones, wirelessly-equipped personal computers or tablets, tracking devices, embedded wireless communication modules, or other devices equipped with wireless communication functionality. In general, each coverage area may operate on one or more carriers each defining a respective bandwidth of coverage, and each coverage area may define an air interface providing a downlink for carrying communications from the base station to UEs and an uplink for carrying communications from UEs to the base station. The downlink and uplink may operate on separate carriers or may be time division multiplexed over the same carrier(s). Further, the air interface may define various channels for carrying communications between the base station and the UEs. For instance, the air interface may define one or more downlink traffic channels and downlink control channels, and one or more uplink traffic channels and uplink control channels.
In accordance with the Long Term Evolution (LTE) standard of the Universal Mobile Telecommunications System (UMTS), for instance, each coverage area of a base station may operate on one or more carriers spanning 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, or 20 MHz, with each carrier in a coverage area defining a respective “cell”. On each such carrier used for downlink communications, the air interface then defines a Physical Downlink Shared Channel (PDSCH) as a primary channel for carrying data from the base station to UEs, and a Physical Downlink Control Channel (PDCCH) for carrying control signaling from the base station to UEs. Further, on each such carrier used for uplink communications, the air interface defines a Physical Uplink Shared Channel (PUSCH) as a primary channel for carrying data from UEs to the base station, and a Physical Uplink Control Channel (PUCCH) for carrying control signaling from UEs to the base station.
A recent revision of LTE known as LTE-Advanced now permits a base station to serve a UE with “carrier aggregation,” by which the base station schedules bearer communication with the UE on multiple carriers at a time. With carrier aggregation, multiple carriers from either contiguous frequency bands or non-contiguous frequency bands can be aggregated to increase the bandwidth available to the UE. Currently, the maximum bandwidth for a data transaction between a base station and a UE using a single carrier is 20 MHz. Using carrier aggregation, a base station may increase the maximum bandwidth to up to 100 MHz by aggregating up to five carriers. Each aggregated carrier is referred to as a “component carrier.”
In practice, base stations may take various forms, such as, for instance, a “macro base station” or “macrocell” implemented in public spaces typically including a cell tower and tower top antenna structure, or a “small cell” that typically has a smaller form factor and is designed to provide smaller coverage. Small cells are low-powered radio access base stations that address gaps in coverage, offload mobile data traffic from other large scale base stations, or both. As a result of growth in mobile data traffic, many service providers strategically provide small cells throughout their coverage areas or offer small cells directly to consumers for use in a home or office. Examples of small cells include femtocells, picocells, and microcells. In general, small cells are smaller in size, weight, and output-power than macro base stations.
Further, each base station in a wireless communication system may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. In an example arrangement, the network infrastructure may include one or more packet data network gateways (PGWs) or similar components that provide connectivity with a packet-switched network so as to support various communication services.
The connection between a base station and other radio access network (RAN) components (e.g., PGWs) situated further towards the network core is commonly referred to as a “backhaul” and may take various forms. For many typical configurations involving macro-type base stations, the backhaul may comprise one or more high-capacity telecommunication trunks, such as T1, millimeter wave, or microwave wave links. Likewise, the backhaul for some small cells may also comprise a T1, millimeter wave, or microwave link. However, for some small cells, the backhaul may take a different form. For instance, some small cells may connect to a service provider's network by way of a residential or commercial broadband connection (e.g., cable line, fiber optic line, Digital Subscriber line (DSL), or the like).